The field of molecular electronics has been driven in part by the prospect that devices that rely on the bulk properties of semiconductors will fail to retain the required characteristics to function when feature sizes reach nanoscale dimensions. As a consequence, there has been much interest in developing molecular-based electronic materials for use in both memory architectures and circuit elements.1 Towards this goal, we have been engaged in a program aimed at constructing devices that use the properties of molecules to store information.2-6 In these approaches, a collection of redox-active porphyrinic molecules attached to an electroactive surface serves as the active storage medium, and information is stored in the discrete redox states of the molecules. The focus of this work has been developing a hybrid architecture, where the molecular material is attached to a semiconductor platform. The implementation of hybrid molecular/semiconductor architectures as a transition technology leverages the vast infrastructure of the semiconductor industry with the advantages afforded by molecular-based active media.
The success of such a hybrid architecture requires, in general, (1) a straightforward means of attaching porphyrins to an electroactive surface, particularly large-wafer silicon, and (2) a robust linkage that can withstand large numbers of redox cycles. A number of methods have been developed for covalent attachment of organic molecules to silicon surfaces.7 For example, the reaction of Si (hydrogen-passivated or chlorine-modified) with an alcohol affords the self-assembled film containing RO—Si linkages. However, the reaction requires use of neat liquids or a very high concentration of the molecules to be attached.8-11 Porphyrins generally have low solubility in organic solutions, with concentrations of ˜50 mM being a typical upper limit. The method we previously developed for attaching porphyrins to Si platforms (either hydrogen-passivated or iodine-modified) involved depositing a drop of solution containing the porphyrin compound in a high-boiling solvent (e.g., benzonitrile, bp 191° C.) onto a photolithographically patterned micron-size Si electrode, followed by heating at ˜170° C. for several hours, during which time additional solvent was added to the sample area.6 This method afforded attachment of porphyrins6 (and ferrocenes3,6) to Si(100) via tethers that are terminated with OH, SAc, and SeAc groups, yielding RO—Si, RS—Si, and RSe—Si linkages (the acetyl protecting group is cleaved upon attachment) where R represents the tether and accompanying redox-active unit.12 This procedure produced high quality monolayers useful for academic studies but was unsuited for reproducible fabrication of memory chips on large Si wafers. In addition, in the past few years it has become apparent that more stable monolayers are generally obtained with carbosilane linkages (RC—Si) than alkoxysilane linkages (RO—Si). Achieving a stable linkage of the redox-active unit to the Si surface is essential because as many as 1015 cycles may be encountered over an operational lifetime in a memory chip.13 
A number of methods have been developed for derivatizing silicon surfaces via carbosilane linkages.7 The methods include pyrolysis of diacyl peroxides,14,15 reaction of Grignard reagents (with halogenated silicon surfaces),16 and electrografting of aryldiazonium salts,17 alkyl halides,18 or Grignard reagents.19 Alkenes have been employed for attachment to Si via thermal,15,20,21 free radical,15 photochemical (UV),22-24 and Lewis-acid mediated reactions.25,26 Alkynes have been less studied but generally appear to react via the same methods as for alkenes, including thermal,27 free radical,15 photochemical,28 Lewis-acid mediated,26,28 and electrografting processes.28 